Compositions designed for use in cleaning, particularly in automatic dishwashing and laundry methods are well known and a consistent effort has been made by detergent manufacturers to improve the cleaning and/or rinsing efficiency of said compositions as reflected by many patent publications.
The satisfactory removal of bleachable soils such as tea, coffee and red wine is a particular challenge to the formulator of a bleaching composition. Traditionally, the removal of such bleachable stains has been enabled by the use of bleach components such as oxygen bleaches, including hydrogen peroxide and organic peroxyacids. The organic peroxyacids are often obtained by the in situ perhydrolysis reaction between hydrogen peroxide and an organic peroxyacid bleach precursor.
Traditionally, the most commonly used source of hydrogen peroxide has been perborate salts, such as sodium perborate monohydrate and tetrahydrate. Percarbonate salts, such as sodium percarbonate are alternative hydrogen peroxide sources which have the advantage of, after release of the hydrogen peroxide, additionally providing carbonate ions to the wash solution. Carbonate ions contribute alkalinity and builder capacity to the solution.
A problem associated with the use of percarbonate bleach is the formation of insoluble carbonate deposits. It is believed that carbonate ions released by the percarbonate bleach during perhydrolysis, complex with cations in the wash solution forming insoluble carbonate deposits. Additionally, once having formed, an initial minor carbonate deposit can act as a "seeding centre" for the formation of a larger, possibly composite, deposit structures, including those associated with redeposition of soils, lime soaps and silicate salts.
Lime soap deposits are most commonly encountered when the washload contains fatty soils, which naturally contain levels of free fatty acids, and when lipolytic enzymes are components of the formulation. Lipolytic enzymes catalyse the degradation of fatty soils into free fatty acids and glycerol. Silicate is a common component of machine dishwashing formulations, where it is added for its china care capability.
Deposit formation can occur on a range of commonly encountered substrate surfaces including fabric, plastic, glass, metal and china surfaces. Certain deposit types however, show a greater propensity to deposit on certain substrates.
The formation of insoluble carbonate, especially calcium carbonate, deposits are a particular problem in the machine dishwashing art. Such deposits are also problematic in laundry washing methods, where the deposits accumulate on the fabric surface (a phenomenon sometimes known as `ash deposition`) thereby causing the fabrics to take on a yellowed or dingy appearance.
The naturally sourced, inlet water to the dishwasher machine can be a sufficient source of Ca.sup.2+ and Mg.sup.2+ ions and CO.sub.3.sup.2- /HCO.sub.3- ions to make deposit formation a problem. Whilst the salt softening system, through which the inlet water will pass prior to entry into the main cavity of a dishwasher machine, can be efficient at removing the naturally present Ca.sup.2+ and Mg.sup.2+ ions it is inefficient at removing the CO.sub.3.sup.2- /HCO.sub.3- ions which therefore enter into the wash/rinse solution.
The Applicants have now established that both the levels of Ca.sup.2+ /Mg.sup.2+ hardness ions and the levels of CO.sub.3.sup.2- /HCO.sub.3- ions in the wash/rinse water of a dishwasher machine are factors controlling calcium carbonate deposit formation. Critical levels of all components must be exceeded for deposit formation to occur. These critical levels are to an extent interdependent. Thus, even in wash/rinse solutions containing high levels of one component, deposit formation will not occur in the absence of the critical level of the other component.
The Applicants have found that the problem of calcium carbonate deposit formation associated with the use of a percarbonate bleach, may be effectively ameliorated by the inclusion of amino tricarboxylic acid (ATCA) into a bleaching formulation.